Heretofore, a hologram record apparatus, which may be provided with a liquid crystal device and the like, irradiates a spatial light modulator for modulating light depending on record information to be recorded, with laser light as signal light. Particularly, in the spatial light modulator, cells are arranged planarly in a matrix so that the signal light is modulated by changing light transmittance of each cell depending on the record information. Furthermore, the modulated light is outputted with different output angles, as a plurality of diffraction light, such as zeroth-order light, or 1st-order light and so on, duo to diffraction phenomenon in the cell having a fine pitch. In this case, the output angle is defined by the cell pitch, which indicates an modulation unit. Then, the signal light modulated with the spatial light modulator constructed as above and reference light not passed through the spatial light modulator are interfered on the hologram record medium. Thereby, the record information is recorded as a wavefront on the hologram record medium.
An angle-multiplex type hologram record apparatus is proposed for multiply recording different information in the same area, by changing little by little a surface angle of the hologram record medium relative to the reference light and the signal light, particularly during recording. In the present application, the angle of the signal light relative to the hologram record medium surface in such an angle-multiplex type recording is referred to as a “record angle” as appropriate. Furthermore, an angle as a standard of the record angle, such as the record angle when it corresponds to a normal line of the hologram record medium surface, is referred to as a “standard record angle”. Still further, in the present application, each record plane corresponding to each record angle is referred to as an “angle record plane”, and a record plane corresponding to the standard record angle is referred to as a “standard angle record plane”.
On the other hand, a hologram reproduction apparatus consisting a pair with the hologram record apparatus is designed to reproduce the record information multiply recorded in the same area, by changing little by little the surface angle of the hologram record medium relative to the reproduction illumination light. In the present application, the angle of the reproduction light relative to the hologram record medium surface in such an angle-multiplex type reproduction is referred to as a “reproduction angle” as appropriate. Furthermore, an angle as a standard of the reproduction angle, such as the reproduction angle when it corresponds to a normal line of the hologram record medium, is referred to as a “standard reproduction angle”.
In the angle-multiplex type hologram record apparatus, recording to each angle record plane in the same record area are successively performed for each record angle, by changing the record angle in the maximum range with increment or decrement 0.01 degree from the standard record angle (e.g. by changing little by little in the range of 88-92 degree). Incidentally, in the present application, an area on the hologram record medium surface onto which the signal light and the reference light are irradiated together is referred to as a “record area”. In the angle-multiplex type recording, a plurality of angle record planes such as 50 planes is recorded in the same record area.
On the other hand, in the angle-multiplex type hologram reproduction apparatus, the record information multiply recorded in the same area is reproduced for each reproduction angle, by changing little by little the reproduction angle from the standard reproduction angle in response to the record angle.
Thus, in the angle-multiplex type hologram record apparatus and hologram reproduction apparatus, the record information can be recorded respectively on a plurality of angle record planes recorded for each record angle in the same record area, and the recorded information can be reproduced respectively. Therefore, record density and recording capacity are expected to be remarkably increased.
In addition to the aforementioned angle-multiplex system, various multiplex systems are proposed, such as a focal-depth-multiplex system for performing multiple recordings with various focal depths of the signal light entering the hologram record medium, a reference light phase-code-multiplex system for performing multiple recordings with various phases of the reference light, a reference light amplitude-multiplex system for performing multiple recordings with various amplitudes of the reference light, a reference light polarization-multiplex system for performing multiple recordings with various polarizations of the reference light and so on. Also in these multiplex systems, since a plurality of record information can be multiply recorded in the same record area, the record density and the recording capacity is expected to be remarkably increased.
Incidentally, in general, it is not practical to perform the multiple recordings onto a whole surface of one hologram record medium at one time, in view of a record plane area of all-purpose size of the hologram record medium, expansion of the signal light and the reference light obtained from an optic system, such as a multi-purpose lens, on the record plane, size or optical performance of a multi-purpose spatial light modulator or lens and so on.
For this, a technology is presented for dividing the record plane of the hologram record medium into a plurality of record areas sized suitably to be irradiated with the signal light and the reference light, performing the multiple recordings as mentioned above for each record area, and after the multiple recordings for one record area is completed, moving to the next record area and starting the multiple recordings and then repeating these processes.